Heart disease is the leading cause of death in the United States. A heart attack (also known as an acute myocardial infarction (AMI)) typically results from a thrombus (i.e., a blood clot) that obstructs blood flow in one or more coronary arteries. AMI is a common and life-threatening complication of coronary heart disease. Myocardial ischemia is caused by an insufficiency of oxygen to the heart muscle. Ischemia is typically provoked by physical activity or other causes of increased heart rate when one or more of the coronary arteries are narrowed by atherosclerosis. Patients will often (but not always) experience chest discomfort (angina) when the heart muscle is experiencing ischemia. Those with coronary atherosclerosis are at higher risk for AMI if the plaque becomes further obstructed by thrombus.
The current treatment for a coronary narrowing (a stenosis) is the insertion of a drug-eluting stent such as the Cypher™ sirolimus-eluting stent from Cordis Corp. or the Taxus™ paclitaxel-eluting stent from the Boston Scientific Co.
Acute myocardial infarction and ischemia may be detected from a patient's electrocardiogram (ECG) by noting an ST segment shift (i.e., voltage change) over a relatively short (less than 5 minutes) period of time. However, without knowing the patient's normal ECG pattern, detection from a standard 12-lead ECG can be unreliable.
Fischell et al. in U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023 describe systems and algorithms for detecting the onset of acute myocardial infarction and providing both treatment and alarming to the patient. In U.S. Patent Application No. 60/524,873, Fischell et al. describe a Guardian system for the long term tracking of myocardial ischemia to provide early prediction of coronary obstruction before the occurrence of a complete coronary artery blockage that results in an AMI.
Fischell et al., in the above references, describes a physician's programmer as a laptop computer like device designed to upload programming to the implant and download electrogram data collected by the implant. Although the parameters to be uploaded from the programmer are described by Fischell et al., the programmer functional screens using a graphical user interface (GUI) to simplify setting the parameters are not discussed. Also not described by Fischell et al. are techniques for display of the multiplicity of recorded electrogram and/or electrocardiogram segment data downloaded from the implant. Finally, Fischell et al. do not describe programmer displays associated with the collection, analysis and display of heart signal parameter histogram data captured over time by the implant.
Although often described as an electrocardiogram (ECG), the stored electrical signal from the heart as measured from electrodes within the body should be termed an “electrogram.” The early detection of an acute myocardial infarction or exercise-induced myocardial ischemia caused by an increased heart rate or exertion is feasible using a system that can detect a change in a patient's electrogram. The portion of such a system that includes the means to detect a cardiac event is defined herein as a “cardiosaver,” and the entire system including the cardiosaver and the external portions of the system is defined herein as a “Guardian system.”
Furthermore, although the masculine pronouns “he” and “his” are used herein, it should be understood that the patient or the medical practitioner who treats the patient could be a man or a woman. Still further the term “medical practitioner” shall be used herein to mean any person who might be involved in the medical treatment of a patient. Such a medical practitioner would include, but is not limited to, a medical doctor (e.g., a general practice physician, an internist or a cardiologist), a medical technician, a paramedic, a nurse or an electrogram analyst.
The term “cardiac event” refers to any specific abnormal action of a patient's heart. ST shift related cardiac events and arrhythmias are cardiac events. ST shift related cardiac events include acute myocardial infarctions or ischemia caused by effort (such as exercise) and/or an elevated heart rate. The ST segment voltage change in ST shift related cardiac events may be either elevation (a positive voltage shift) or depression (a negative voltage shift). Arrhythmias include bradycardia, tachycardia or an arrhythmia such as atrial fibrillation, atrial flutter, ventricular fibrillation, and premature ventricular or atrial contractions (PVCs or PACs, respectively).
For the purpose of this invention, the term “electrocardiogram” is defined to be the heart's electrical signals sensed by one of more skin surface electrodes that are placed in a position to indicate the heart's electrical activity (depolarization and repolarization). An electrocardiogram segment refers to the recording of electrocardiogram data for either a specific length of time, such as 10 seconds, or a specific number of heart beats, such as 10 beats. For the purposes of this specification, the PQ segment of a patient's electrocardiogram is the typically flat segment of a beat of an electrocardiogram that occurs just before the R wave.
For the purpose of this invention, the term “electrogram” is defined to be the heart's electrical signals from one or more implanted electrode(s) that are placed in a position to indicate the heart's electrical activity (depolarization and repolarization). An electrogram segment refers to the recording of electrogram data for either a specific length of time, such as 10 seconds, or a specific number of heart beats, such as 10 beats. For the purposes of this specification, the PQ segment of a patient's electrogram is the typically flat sub-segment of an electrogram that occurs just before the R wave. The ST segment is the sub-segment of an electrogram that begins shortly after the R wave and ends just before the T wave (or it may include all or part of the T wave). A beat is defined as a sub-segment of an electrogram or electrocardiogram segment containing exactly one R wave. ST and PQ segments of a beat within an electrogram segment are defined herein as sub-segments of the electrogram segment. For the purposes of this specification, the terms “detection” and “identification” of a cardiac event have the same meaning.
Heart signal parameters are defined to be any measured or calculated value created during the processing of one or more beats of electrogram data. Heart signal parameters include PQ segment average value, ST segment voltage average value, R wave peak value, ST deviation, daily median ST deviation, daily mean ST deviation, ST shift, average signal strength, T wave peak height, T wave average value, T wave deviation, heart rate and R-R interval. ST segment voltage average value, ST deviation, daily median ST deviation, daily mean ST deviation, and ST shift are examples of ST segment related measurements.